Fix reflection component removal

[vincentfretin]

Description:

We get a Uncaught TypeError: this.removeChild is not a function error when removing the scene if we had the reflection component on it and we didn't enter vr mode.

Changes proposed:

• Be sure this.probeLight exists before trying to remove it, also use this.el.removeChild instead of non existing this.removeChild
• Add a test that doesn't fail on this error

[vincentfretin]

I prefer to declare the variable in init like this. Also I check for it in the test.

[dmarcos]

Do we need to declare it?

[vincentfretin]

No, we don't need to declare it. There is also other variables used on this that are not declared either.

[vincentfretin]

We use scene.environment = null three line above, we should use the scene variable here for symmetry :)

[vincentfretin]

this.probeLight = null; is not mandatory, but I find it good code hygiene to remove any reference to a DOM element explicitly. This can help the GC too.

[dmarcos]

This should probably be undefined. null represents a missing object. In this case we're resetting the variable. Also for style consistency

[vincentfretin]

I removed the line. This doesn't add much. The component is removed anyway, so the DOM element is removed as well.

[vincentfretin]

About null vs undefined, please note that in the aframe code base we are currently setting some variable to null in remove like I suggested. In the text component for example:

aframe/src/components/text.js

Lines 126 to 135 in 579473b

	remove: function () {
	this.geometry.dispose();
	this.geometry = null;
	this.el.removeObject3D(this.attrName);
	this.material.dispose();
	this.material = null;
	this.texture.dispose();
	this.texture = null;
	if (this.shaderObject) { delete this.shaderObject; }
	},

[dmarcos]

Thank you!